Dear Aunt Sue and Uncle Marshall,I just met Jan & Pete as well all jet off to Europe. They tell me you are a lovely couple and they seem to genuinely appreciate your generous gift of a new microwave. I'm sure they very much enjoyed seeing you at the wedding and only regret they couldn't chat with you longer to tell you about their seating assignments for the 6 hour flight to their honeymoon. I will think of you fondly as I make my sales presentation to the overseas market.Warmest regards,WillyNilly, seat 16A

I was about to suggest writing something similar and then sealing the envelope, but I couldn't have composed something as perfect as this!